You are dealing with a freshman in college.
I deal with it all the time in a major regional theatre.
There are actors in the world who will not take notes form a stage manager, an assistant director or anyone who tries to give them notes during the run of show.
Sadly, it's a fact of life.
You can hope in the end they won't get hired agian.
But sadly, they do over and over.
The best thing to do is to notify is remember that ultimately stage management is middle management, and report the issue to someone above you.
Birdie was right, often actors don't want to take a note form someone they view as a peer, like a stage manager, or someone who they view is under them, which a lot of actors someitmes view a stage manager. Again, there are all types of actors out there.
No names mentioned. (Just wanted to point that out)